PARIS  French voters dealt a stinging warning to President Nicolas Sarkozy by throwing his party out of office in a string of towns and cities, a ballot box setback that prompted immediate promises of reinvigorated reforms from his government.

While of only limited national import, the reverses in municipal elections Sunday for mayors and city councilors were a sobering reminder of how the 53-year-old Sarkozy has shrunk in the estimation of some voters since he was elected last May on a program of in-depth economic and social change for France.

Then, Sarkozy was welcomed like a rock star by tens of thousands of cheering supporters in Paris. On Sunday night, as results showed that his party had lost control of closely-watched towns and cities, he did not make an appearance -- leaving his prime minister, Francois Fillon, to defend his policies in a televised declaration.

Fillon vowed to stay the course of reform despite demands for a change of tack from opposition Socialists buoyed by their showing in the elections. Fillon promised stepped-up efforts to create jobs and fatten paychecks -- both leading demands of the French.

"You can't change a great country like ours in a few months," he said. "Tenacity is needed to reform."

From foie gras country in the southwest to Champagne country in the northeast, towns where Sarkozy's UMP party had been in charge swung to the opposition Socialists.

Sarkozy was expected to make changes in the government and his personal team, likely within days, while avoiding a major ministerial reshuffle. One minister sure to be replaced was Christian Estrosi, in charge of overseas territories, who was elected mayor of Nice. He had promised to leave the government to be full-time mayor if elected.

UMP leader Patrick Devedjian said Monday that changes would be small "and above all technical."

Presidential spokesman David Martinon, disgraced after an internal party rebellion forced him out of the mayoral race in Sarkozy's fiefdom of Neuilly-sur-Seine, was expected to lose his job at the president's side.

Reeling since Sarkozy defeated their candidate, Segolene Royal, last May, the Socialists could now bounce back as more of a coherent, forceful opposition to Sarkozy on the back of the municipal results.

Paris stayed in the hands of Socialist Mayor Bertrand Delanoe, City Hall said, and Lyon also was in Socialist control.

In Perigueux, Sarkozy's minister for education, Xavier Darcos, lost his bid to be re-elected as mayor -- by 113 votes.

A Socialist took control of the important conservative bastion of Toulouse, home to plane maker Airbus, according to the Interior Ministry.

The ministry's official results showed conservatives and centrists lost mayorships in Strasbourg, Blois, Reims, Caen and Amiens. Projections by the polling agencies Ipsos and TNS-Sofres showed other towns set to switch to leftist hands.

There was one bright spot for Sarkozy's party: Its candidate, incumbent mayor Jean-Claude Gaudin, won a tough and crucial contest in Marseille, he and his opponent said. Losing the port city would have been a big blow for the UMP.

Looked at nationally, partial official results showed parties of the left leading slightly, with 48.7 percent of the overall vote to 47.6 percent for the right.

Sarkozy has been beset by low poll ratings and complaints from opposition politicians and voters alike that he has acted in a manner unbefitting for a president with a series of angry public outbursts, a widely publicized divorce, and a quick courtship and marriage to former model and singer Carla Bruni.

Ten months after his election, France's economy remains sluggish and Sarkozy has backed off from or toned down some of the sweeping reforms that he promised on the campaign trail last year.

Internationally, this year is a crucial one for his presidency: France takes over the rotating presidency of the European Union in July, which will put Sarkozy's leadership even more in the spotlight.

Looking to capitalize on their showing, leading Socialists insisted that the two rounds of voting over two weekends across the country and in France's far-flung overseas territories represented a major setback for Sarkozy's politics.

Socialist former Prime Minister Laurent Fabius said the government was heading for "divorce" with the French electorate if it refuses to change its policies. He used a soccer metaphor to characterize Sunday's results, saying voters had given the government "a red card."

The municipal elections have less to do with party affiliation than other elections, and most voters say they cast their ballots based on local issues like parks, public transport and garbage collection. Yet the race was also a gauge of how the French rate Sarkozy's performance.

Bruno Marcandella, a computer engineer from Paris' Latin quarter, expressed dissatisfaction with the way Sarkozy handles "everything -- not just his personal life."

"I'm going to vote because I want my vote to count on a national level," he said.

Socialist Mayor Bertrand Delanoe, center, surrounded by his staff, reacts after he was re-elected with 57,7% of the votes as Mayor of Paris at the City Hall in Paris, Sunday, March 16, 2008.(AP Photo/Michel Euler)